1. Field of the Invention
The present invention relates to optical components for applications in integrated optics. These components may be active or passive components such as second harmonic generators, electrooptical modulators, electrooptical couplers or electrooptical switches with n inputs and n outputs.
2. Description of the Prior Art
There are known second harmonic generators for integrated optics formed by structures based on lithium niobate LiNbO.sub.3 or formed by organic materials. These structures are constituted by a succession of microdomains with a pitch equal to the length of coherence: ##EQU1## wherein each domain is polarized in reverse with respect to the neighboring domain. This enables a partial overlapping of the phases of the incident wave (with a pulsation .omega.) and the created wave (with a pulsation 2.omega.). It is possible, notably, to double the infrared frequency (.lambda.==0.86 .mu.m) to obtain a blue light (.lambda.=0.43 .mu.m) with an LnNbO.sub.3 structure formed by about a hundred domains (See the article by G. A. Magel, M. M. Fejer and R. L. Byer, "Second Harmonic Generation Of Blue Light In Periodically Poled Lithium Niobate", Cleo '89/Thursday Afternoon/350). It is also known that it is possible to make an organic structure that generates red light (.lambda.=0.63 .mu.m) and is formed by 300 inverted microdomains (see the article by G. Khanarian, D. Haas, R. Keosian, D. Karim and P. Landi, "Phase-Matched Second Harmonic Generation In A Polymeric Waveguide", Cleo '89/Thursday Morning/254).
With respect to the switches and the electrooptical modulators for integrated optics, the main structures used are complex structures on LiNbO.sub.3 where the optical guides are formed by titanium doping. However, since it is not possible to obtain any thin layer of monocrystalline LiNbO.sub.3, it is not possible to make any electrooptical modulator with facing electrodes. The electrodes are then arranged in a coplanar way, thus reducing the efficiency of the lithium niobate.
Recently, a first polymer-based electrooptical modulator has been developed and disclosed by the Lockheed Missiles And Space Company Inc. (Cf. R. Lytel, G. F. Lipscomb, M. Stiller, J. I. Thackara, A. J. Ticknor, Organic Integrated Optical Devices). It has been shown that the light can be confined laterally by simple localized polarization of an active layer. The variation in index obtained is of the order of 10.sup.-3 to 5.10.sup.-2 : this is sufficient to obtain a lateral confinement.
The present invention concerns the making of optical components for applications in integrated optics such as the modulation of light and the generation of second harmonics by means of stacks of three carefully chosen polymer layers. Two of these layers are passive and have an optical index that is low enough to confine the optical mode in the central layer which has a high optical index and is formed by an active material. By acting locally on the index of one of the three layers, we obtain a lateral confinement of the light wave.